In general, an antenna is a conversion device for transmitting or receiving an electromagnetic wave of a specific band. The antenna serves to convert an electrical signal of a radio frequency band to an electromagnetic wave or, conversely, serves to convert an electromagnetic wave to an electrical signal. Such an antenna is widely used for a device for receiving radio broadcast, a television broadcast or the like, a radio set using radio waves, a wireless LAN two-way communication device, a radar, a radio wave telescope for space exploration, and so forth. Physically, an antenna is an array of conductors for radiating n electromagnetic field generated when a certain voltage is applied together with a modulated current. A current and a voltage induced in an antenna under the influence of an electromagnetic field are generated between the terminals of the antenna.
A conventional substrate for supporting an antenna pattern has via-holes vertically penetrating the substrate. However, it is difficult to individually process and form such via-holes. Korean Patent No. 10-1399835 discloses a technique on an antenna using a porous aluminum oxide layer. More specifically, the patent cited above discloses a wireless communication device case made of aluminum. The wireless communication device case includes an insulating region having a first porous layer and a second porous layer. The first porous layer includes a first groove formed by anodizing an inner surface of a predetermined region of the case and a first barrier layer as an alumina layer formed around the predetermined region. The second porous layer includes a second groove formed by anodizing an outer surface of the case corresponding to the predetermined region and a second barrier layer as an alumina layer formed around the second groove. The wireless communication device case further includes an antenna pattern formed on the first porous layer and configured to receive radio waves. The first barrier layer and the second barrier make contact with each other in the thickness direction of the case.
However, in the technique of the above-cited patent which utilizes a porous aluminum oxide layer in the field of an antenna, no metallic material is filled in the porous aluminum oxide layer. Thus, the surface area of the porous aluminum oxide layer is small and the impedance thereof is low. In addition, it is required to provide an additional means for cutting off external radio waves introduced from the side surface.